Bearing device, in particular for a shaft of a turbocharger, and turbocharger having such a bearing device

ABSTRACT

A bearing device ( 1 ), in particular for a shaft ( 2 ) of a turbocharger ( 3 ), including two journal bearings ( 5 ) and a bush-like separating element ( 9 ) for spatially separating the two bearings ( 5 ). The separating element ( 9 ) includes a separating bush which is formed in the manner of a cage having a multiplicity of apertures ( 16 ) arranged circumferentially and separated from one another by struts ( 17 ).

The present invention relates to a bearing device, in particular for ashaft of a turbocharger, including two journal bearings and a bush-likeseparating element for spatially separating the two bearings. Thepresent invention also relates to turbocharger having such a bearingdevice.

Such an assembly is used, inter alia, in the manufacture of engines.Here, for example, the turbine shaft of an exhaust-gas turbochargerrests in such a bearing device.

BACKGROUND

A bearing device of this type is disclosed in European Patent DocumentEP 03 95 825 B1. There, a separating element referred to as spacer isdescribed, which has a hollow cylindrical main body whose the outercircumferential surface is provided with guide devices which projecttherefrom for guiding the spacer within a bearing bore. In a preferredembodiment, there is further provided a central outlet opening whichpermits oil within the spacer to pass radially outward therethrough.Here, however, the oil-holding capacity is quite low, and themanufacture of such a spacer is relatively expensive because it istypically made by lathing.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved bearingdevice that is less expensive to manufacture.

The present invention provides a bearing device that is composed of atleast two journal bearings and a bush-like separating element whichspatially separates the two bearings. Such a bearing device is intended,in particular, for a shaft of a turbocharger, where the bearings usedare typically plain journal bearings. The separating element of thisassembly includes a separating bush which is formed in the manner of acage having a multiplicity of apertures arranged circumferentially andseparated from one another by struts. The cage-like structure of theseparating bush allows a significant reduction in material use, and thusalso a reduction in weight of the separating element. While thereduction in material use is associated with a reduction inmanufacturing cost, the weight reduction also makes it possible, forexample, to reduce fuel consumption when the bearing device is used in avehicle. In addition, if oil lubrication and, in particular, floatingsupport are provided for the device, then the corresponding aperturesprovide improved lubrication efficiency since, depending on theoperating state, the apertures act either as pockets for intermediatestorage of oil, or as enlarged openings in a flow path of thelubrication oil.

Preferably, the separating element has a larger inner diameter than thetwo bearings. Since the separating element is not intended to perform asupporting function for the shaft, a further reduction of both weightand material use is achieved in this manner. In addition, the space socreated between the separating element and the shaft is used, forexample, as an additional intermediate storage for lubrication oil.

It is also advantageous to adapt the shape of the apertures to theintended use of the bearing device. Therefore, it is preferred for theapertures to be, for example, bar-shaped to match the typicallyelongated shape of the separating element. More specifically, here theapertures are configured such that their dimension in the direction ofthe longitudinal center axis of the shaft is at least a factor of 2,preferably a factor of 5, larger than their dimension perpendicularthereto.

Further, in an advantageous embodiment, the elongated apertures, andthus also the struts, are oriented substantially parallel to thelongitudinal center axis of the shaft. This achieves, for example,increased resistance to axial loads.

In addition, the number of formed apertures exceeds, for example, avalue of 3, and preferably a value of 5. In this connection, the aim isalways to achieve the best possible compromise between weight reductionand resistance to stresses in order to ensure a long life for thebearing device.

In accordance with another preferred embodiment, a roller bearing cage,in particular, a needle roller bearing cage, is used the separatingbush. Such bearing cages are mass-produced in very large quantities andcommercially available also in suitable dimensions. Such designs arewell-known to those skilled in the relevant art and described in detail,for example, in German Patent Documents DE 00 00 01 009 445 A, DE 00 0001 022 431 A and DE 00 00 01 079 901 A. In a variant, the separatingelement has a multi-part design, and a suitable bearing cage is used asthe separating bush. The separating bush may then be completed, forexample, by simple annular members to forma separating element, if it isonly the axial dimension of the separating bush that is not suited forthe intended application. However, it is preferred for the separatingelement to be made as a single part, where the separating bush alone, inparticular a bearing cage, functions as the separating element. Overall,this provides the advantages of a low manufacturing cost, easy assembly,and favorable performance characteristics. The low cost is achieved, inparticular, using the principle of shared identical parts; i.e, by usingthe bearing cage, which is already available for other purposes andwhose manufacture is cost-optimized by producing it in large quantities,for example, as a stamping.

In a preferred embodiment, the two bearings and the separating elementare fixed in position by an axial press-fit. This makes it possible, forexample, to provide a circumferential clearance around these components,which is filled with a lubrication oil. Due to the apertures in theseparating element, this oil is then able to wet, as leakage flow, themating contact surfaces between the shaft and the bearings. In this way,a so-called “floating support” is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present invention is described below withreference to several drawings, in which:

FIG. 1 is a cross-sectional view of a turbocharger having a bearingdevice according to the prior art;

FIG. 2 is a side view showing a roller bearing cage according to theprior art;

FIG. 3 is a cross section along line III-III of FIG. 2 showing theroller bearing cage according to the prior art;

FIG. 4 is a cross-sectional view showing a bearing device according tothe present invention along with a turbocharger shaft supported therein;and

FIG. 5 is a cross-sectional view showing the bearing device according tothe present invention without the turbocharger shaft.

Like parts are identified by the same reference numerals in all figures.

DETAILED DESCRIPTION

In the exemplary embodiment described hereinbelow, a bearing device 1serves by way of example to support a shaft 2 (see FIG. 4) of anexhaust-gas turbocharger 3. Such an exhaust-gas turbocharger 3 is shownin FIG. 1 along with a bearing device 1 according to the prior art.Shaft 2 (not shown in this figure) has a turbine wheel 4 attached toeach of its ends.

Two plain journal bearings 5 are positioned within a receiving space 6in housing 7 of turbocharger 3 to support shaft 2. The two plainbearings 5 are fixed in position by means of an axially actingpress-fit, which is provided by an abutment 8 disposed at each of theends on the one hand and by a hollow cylindrical separating element 9 onthe other hand. Separating element 9 is typically made by lathing and istherefore relatively expensive to manufacture. Radially extending andcentrally positioned openings are provided to function as part of alubrication oil flow path for both the plain bearings 5 and theseparating element 9. The corresponding lubrication oil is introduced atoperating pressure into a pre-chamber 11 via a hydraulic network bymeans of a feed pump in a manner not specifically shown. From there, thelubrication oil flows through feed channels 12 to openings 10. Thelubrication oil supplied in this way forms a leakage flow which providesa lubricating film between the mating contact surfaces of the two plainbearings 5 and shaft 2. This lubricating film spreads out towardseparating element 9 and is finally discharged through openings 10therein into a discharge chamber 13, from where it is returned to thehydraulic network.

In order to improve the known bearing device, the component used asseparating element 9 is substituted. In the exemplary embodiment, thiscomponent is replaced by a needle roller bearing cage 14 which, contraryto its intended use as a rolling-element carrier, is used in the bearingdevice as a separating element 9 to spatially separate two plainbearings 5. Due to the cage-like structure, needle roller bearing cage14 both has a low weight and is resistant to mechanical stresses whichmay occur. In addition, the apertures, which form part of thelubrication oil flow path, provide improved lubrication oil flow.

In FIG. 2 and FIG. 3, such a needle roller bearing cage 14 isillustrated by way of example. This bush-like needle roller bearing cage14 has six apertures 16, which are oriented parallel to its longitudinalcenter axis 15 and separated from one another by approximatelybar-shaped struts 17. Since needle roller bearing cage 14 has suitabledimensions, it replaces separating element 9 completely, so that in thisexemplary embodiment, the separating element 9 of the present inventiondoes not include any additional components.

The so-implemented bearing device 1 and its immediate surroundings areshown in FIG. 4 along with shaft 2 and in FIG. 5 without shaft 2. As inthe prior art embodiment shown in FIG. 1, the bearing device of thepresent invention is provided with oil lubrication. In this connection,both plain bearings 5 and needle roller bearing cage 14 are supportedcentrically and with radial clearance in receiving space 6, which iscompletely flooded with lubrication oil when in an operating state.Here, too, feed channels 12 serve for the supply of lubrication oil.However, in needle roller bearing cage 14, apertures 16 assume thefunction of openings 10 in separating element 9. The lubrication oilthat is forced between the mating contact surfaces of shaft 2 and plainbearings 5 and reaches needle roller bearing cage 14 exits through theseapertures.

LIST OF REFERENCE NUMERALS

1 bearing device

2 shaft

3 exhaust-gas turbocharger

4 turbine wheel

5 plain bearing

6 receiving space

7 housing

8 abutment

9 separating element

10 opening

11 pre-chamber

12 feed channel

13 discharge chamber

14 needle roller bearing cage

15 longitudinal center axis

16 aperture

17 strut

1-10. (canceled)
 11. A bearing device comprising: two journal bearings;and a separating bush for spatially separating the two bearings, theseparating bush formed as a cage having a plurality of aperturesarranged circumferentially and separated from one another by struts. 12.The bearing device as recited in claim 11 wherein the separating bushhas a larger inner diameter than the two bearings.
 13. The bearingdevice as recited in claim 11 wherein the apertures are bar-shaped. 14.The bearing device as recited in claim 11 wherein the apertures areconfigured such that their dimension in the direction of thelongitudinal center axis of the shaft is at least a factor of 2 largerthan their dimension perpendicular thereto.
 15. The bearing device asrecited in claim 14 wherein the factor is at least a factor of
 5. 16.The bearing device as recited in claim 14 wherein the apertures areoriented parallel to a longitudinal center axis.
 17. The bearing deviceas recited in claim 11 wherein at least 3 apertures are provided. 18.The bearing device as recited in claim 11 wherein the separating bush isa roller bearing cage.
 19. The bearing device as recited in claim 18wherein the roller bearing cage is a needle roller bearing cage.
 20. Thebearing device as recited in claim 11 wherein the separating bush ismade as a single part.
 21. The bearing device as recited in claim 11wherein the two bearings and the separating element are fixed inposition by an axial press-fit.
 22. A turbocharger comprising thebearing device as recited in claim
 11. 23. The turbocharger as recitedin claim 22 further comprising a shaft, the bearing device being for theshaft.